The present invention relates to a high pressure gas supplying system for supplying, for example, a fuel cell with high pressure gas stored in high pressure tanks.
In recent years, fuel cell powered electric vehicles have been drawn attention from a viewpoint of environmental protection, such as for restricting an emission amount of carbon dioxide, which causes the global warming. The fuel cell powered electric vehicle is furnished with a fuel cell generating electricity by way of electrochemically reacting hydrogen with oxygen that is contained in the air so that electricity generated by the fuel cell is supplied to the motor to generate a driving force. The hydrogen utilized for the fuel cell powered electric vehicle is of gaseous type because of its simple handling compared with the liquid type hydrogen, and a high pressure tank or high pressure gas storage tank is employed as a storage means. Hydrogen powered vehicles have also been drawn attention from the environmental point of view. The hydrogen powered vehicle is equipped with an internal combustion engine for burning hydrogen gas instead of gasoline. The hydrogen powered vehicle is also furnished with a high pressure tank for the same reason as mentioned above.
For the purpose of decreasing the weight, the high pressure tank is mainly made of the plastic, such as polyethylene, and is reinforced by fibers to ensure sufficient withstand pressure. When hydrogen gas is used and the high pressure tank is emptied, the high pressure tank is refilled with hydrogen gas from a hydrogen gas supplying source provided at a hydrogen gas station like a petrol station. The fuel cell powered electric vehicle carries a plurality of high pressure tanks, and selectively or simultaneously, hydrogen gas is supplied to the fuel cell from each tank.
As a known example of the high pressure gas supplying system, Japanese Laid-open Patent Publication No. Hei-8-177641 discloses a high pressure gas supplying system, from which high pressure gas is supplied to a fuel cell and to which high pressure gas is filled.
This high pressure gas supplying system includes a supplying line for supplying the fuel cell with high pressure gas from two high pressure tanks, and a filling line for filling the high pressure tanks with high pressure gas. And the main structural pets of the supplying line and the filling line are shared. The supplying line and the filling line are substantially the same in constitution, except for the constitution in the proximity of the high pressure tanks, where the filling line has a piping line provided with a check valve and the supplying line has a piping line provided with a switch valve. Further, these piping lines are arranged in parallel such that the supply of the high pressure gas from the high pressure tanks to the fuel cell is controlled by the switch valve and the filling of the high pressure gas into the high pressure tanks is controlled by the check valve. According to this high pressure gas supplying system, the check valve prevents a counterflow of the high pressure gas filled in the high pressure tanks into the common part shared by the supplying line and the filling line. Since the piping line with the check valve and the piping line with the switch valve are joined into one piping and connected to the high pressure tank, each high pressure tank has only one connecting opening.
However, in such a high pressure gas supplying system, when these switch valves are released with the internal pressure of one high pressure tank being higher and the internal pressure of the other high pressure tank being extremely lower, the high pressure gas stored in the high pressure tank and having higher internal pressure often counterflows rapidly through the piping and the switch valve into the high pressure tank having lower internal pressure. In this instance, when the high pressure gas contains a lot of hydrogen, heat is generated mainly due to adiabatic compression of the hydrogen gas. Also, due to expansion explained by Joule-Thomson effect, heat is generated. Accordingly, when high pressure hydrogen gas counterflows rapidly into the high pressure tank with smaller internal pressure, the temperature in the high pressure tank rises rapidly. As a result, the high pressure tank and equipment thereof are often damaged. Herein, Joule-Thomson effect explains temperature change of a gas upon adiabatic irreversible expansion of the gas. Adiabatic irreversible expansion of the hydrogen gas becomes an exothermic reaction factor under the ordinary temperature.
As mentioned above, if there is a difference in internal pressure, even it the switch valve is closed at the high pressure tank with lower internal pressure, the check valve opens as in the case of filling high pressure gas. Therefore, there is a possibility that the high pressure gas with higher pressure counterflows into the high pressure tank with lower internal pressure.
Accordingly, the object of the present invention is to provide a high pressure gas supplying system wherein even if there is a pressure difference between a plurality of high pressure tanks to be filled with a high pressure gas mainly composed of hydrogen gas, a counterflow of the high pressure gas from a high pressure tank with higher internal pressure to a high pressure tank with lower internal pressure can be prevented, and hence an unnecessary temperature increase of the high pressure tank can be prevented.
According to the present invention, there is provided a high pressure gas supplying system including:
a plurality of high pressure tanks for filling high pressure gas;
a supplying line for supplying the high pressure gas from the high pressure tanks: and
a switch valve for controlling open/close of each high pressure tank.
wherein the supplying line comprises a plurality of supply piping lines each connected to the high pressure tank, a piping joint section connecting these supply piping lines, and a counterflow preventing section for preventing a counterflow of the high pressure gas from the piping joint section to each high pressure tank.
In this the high pressure gas supplying system, since a counterflow preventing section is provided, the high pressure gas supplied from each high pressure tank can be flown in a certain direction. Therefore, even if there is a pressure difference between high pressure gases filled in the respective as high pressure tanks, it is possible to prevent a counterflow of the high pressure gas having higher pressure into the high pressure tank with lower internal pressure via the piping joint section. Accordingly, since the high pressure gas mainly composed of hydrogen gas does not counterflow into the high pressure tank with lower internal pressure during the supply off the high pressure gas, rapid increase of the high pressure and the high pressure tank can be prevented.
In the aforementioned high pressure gas supplying system, the counterflow preventing section may be formed by a check valve provided either between the piping joint section and each high pressure tank or at each high pressure tank.
Since a check valve has a structure allowing a flow of gas in one direction only, providing a check valve between the piping joint section and the high pressure tank can reliably stop a flow of the high pressure gas counterflowing in the supplying line irrespective of a pressure difference of the high pressure gas in the respective high pressure tanks. Also, the above effect can be achieved if a check valve is provided at a plug of each high pressure tank.
Further, in the aforementioned high pressure gas supplying system, the counter flow preventing section may be formed by a three way valve provided at the piping joint section.
A three way valve has three ports connectable to piping lines and a connection is made with respect to one particular joint by selecting one port from the other two remaining ports. If a three way valve is provided at the piping joint section, for example, one piping line is selected from two piping lines connected to two high pressure tanks among a plurality of high pressure tanks and is connected to the remaining one piping line. Therefore since the non-selected piping line is shut off from the flow of the high pressure gas, the high pressure gas does not counterflow into the non-selected piping line. When necessary, by the combination of such three way valves, it is possible to select a high pressure gas supplying line from two or more high pressure tanks.